Tetraalkylcyclobutane-1,3-diols can be important intermediates for producing a variety of polymeric materials which possess advantageous properties. For example, polyesters derived from dicarboxylic acids and 2,2,4,4-tetramethylcyclobutane-1,3-diol can possess higher glass transition temperatures, impact strength, weatherability, and hydrolytic stability in comparison to many polyesters prepared from other commonly-used diols. Tetraalkylcyclobutane-1,3-diols can be prepared by the catalytic hydrogenation of the corresponding 2,2,4,4-tetraalkylcyclobutane-1,3-dione (I) to the corresponding 2,2,4,4-tetramethylcyclobutane-1,3-diol (II), as illustrated in FIG. 1, in which R is an alkyl group.
Tetraalkylcyclobutanediols typically are produced by hydrogenation of the corresponding tetraalkylcyclobutanediones using a variety of catalysts such as, for example, nickel, ruthenium, and cobalt. For example, the hydrogenation of 2,2,4,4-tetramethylcyclobutane-1,3-dione to 2,2,4,4-tetramethylcyclobutane-1,3-diol can be carried out using nickel- or ruthenium-containing catalysts as described in U.S. Pat. Nos. 3,000,906, 3,190,928; 5,169,994; 5,258,556; and 2,936,324. The hydrogenation of 2,2,4,4-tetramethylcyclobutane-1,3-dione to 2,2,4,4-tetramethylcyclobutane-1,3-diol also can involve cobalt-containing catalysts. For example, U.S. Pat. Nos. 5,528,556 and 5,169,994 disclose that Raney cobalt is effective for hydrogenation of 2,2,4,4-tetramethylcyclobutane-1,3-dione to 2,2,4,4-tetramethylcyclobutane-1,3-diol.
It is known, however, that the nature of the catalyst support can influence catalyst activity and selectivity. For example, catalyst support materials such as alumina, titania, and silica-alumina can have acidic properties that, in turn, can catalyze side-reactions and reduce yield. In particular, 2,2,4,4-tetraalkylcyclobutanediones and their corresponding diols can be sensitive to acid catalysts, which can promote their decomposition into various by-products. Other attributes of the catalyst support, such as porosity, also can affect catalyst activity and selectivity. Some catalyst supports such as, for example, activated carbon, zeolites, and clays may be obtained or derived from natural sources and can have inconsistent properties and quality. There is a need, therefore, for new catalysts for the hydrogenation of 2,2,4,4-tetraalkylcyclobutane-1,3-diones and other sensitive substrates that show good activity and selectivity and can be prepared with consistent properties.